Museo Galileo
Virtual Museum
Hero of Alexandria
1st C. C.E.

Hardly anything is known about Hero's life. The century in which he lived was identified by dating a lunar eclipse observed by him to March 13, 62 C.E. Mathematician and engineer, taught technical subjects at the famed Museum of Alexandria. A careful reader of Ctesibius and Philo, Hero also made a close study of the works of Euclid and Archimedes, from which he drew fruitful lessons. The author of many treatises, Hero forcefully asserted the need for comprehensive training that combined theory and practice. In his mathematical and geometrical works (Definitiones, Geometria, Geodaesia, Stereometrica, Mensurae, Metrica), Hero proposed brilliant systems to solve measurement problems, illustrated the invention of a method to approximate square roots and cubic roots of numbers that are not perfect squares and cubes, and identified the formula (known as Hero's formula) to determine the area of a triangle from its sides. Thanks to a Latin version of the Catoptrics, we know that Hero made another noteworthy contribution to optics by correctly defining the laws of reflection. In his treatise on Dioptrics, Hero described the use of a theodolite of his invention; there is also a chapter on astronomy in which he provided the method for computing the distance between two cities - Rome and Alexandria - from the difference between the local hours at which a lunar eclipse was observed.

Hero also wrote treatises on specific disciplines. The Pneumatics, now regarded as a work of great significance, opens with a theoretical introduction followed by the description of many devices powered by water pressure, steam, and compressed air. The author displays his skills as inventor, describing apparatuses such as the Aeolus cell and what came to be known as Hero's fountain. The Aeolus cell or Aeolus sphere demonstrates how thermal energy can be converted into mechanical energy by harnessing the pressure generated by heating water inside a metal sphere.

Hero also left a treatise On the construction of war machines. His work On automata describes small automated stages that could be set in autonomous rectilinear or circular motion for the entire duration of a theatre performance.

Hero's masterpiece, however, is the treatise on Mechanics, which has come down to us only in Arabic translation. In this work, the Alexandrian scientist offered the first definitive framework for theoretical and practical mechanics by stating that all five basic machines - the lever, the winch, the pulley, the screw, and the wedge - operated on the basis of the lever principle. There are also surviving fragments of Hero's writings on Water clocks, and Commentaries on Euclid's Elements.

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